1. Field of the Invention
This invention relates generally to the pouring of molten metals from a vessel and, more particularly, to contact pouring wherein the vessel is brought in contact with a mold for pouring.
2. Discussion of the Related Art
Devices for pouring molten metals are generally known in the art. Historically, the pouring of gray, malleable and ductile iron into sand molds was done by hand using a pouring ladle. Today, hand pouring has been in part substantially replaced by the use of pressure pouring vessels. These pressure pouring vessels are typically equipped with a stopper rod which enables the molten metal to pour out an orifice in a nozzle when the stopper rod is raised and pressure is applied within the vessel.
In the typical pressure pouring vessel, it is desirable to reduce the velocity of the molten metal as the molten metal enters the mold, which is known in the art as metal impingement velocity. To achieve this, the stopper rod in the pouring vessel is positioned as close to the top of the mold as possible. However, this distance must be sufficient enough to allow for the next mold in line to be moved into place easily. In addition, when the last molten metal exits the nozzle as the stopper rod is closed, the exiting molten metal tends to freeze and buildup on the nozzle. This buildup thus requires an additional clearance between the pouring vessel and the mold to enable the nozzle to be manually cleaned, while the entire pouring operation is stopped. Moreover, as the molten metal exits the pressure pouring vessel, the molten metal freely travels through the atmosphere before eventually entering the mold which causes unwanted oxidation of the metal. Thus, the greater the distance between the pouring vessel and the mold the greater the oxidation.
After the molten metal exits the pressure pouring vessel, it is generally directed into a pouring basin which is cut atop the mold. The pouring basin serves no purpose other than to act as an open end of a funnel to facilitate the pouring of all the metal into the mold. This pouring basin is fitted or connected to a sprue or canal which directs the molten metal into a casting cavity within the mold. The sprue is typically tapered to control the flow of the molten metal into the mold. Since the casting cavity is generally filled from the bottom, the height difference between the molten metal level in the casting cavity and the top of the molten metal in the pouring basin determines the rate at which the mold is filled. Consequently, the pouring operation must be initially fast in order to fill the sprue and the pouring basin. Thereafter, the pouring operation must be progressively slowed down to match the mold fill rate so as to not pour molten metal out or atop the mold.
The closer the casting cavity is located to the top of the mold, the more difficult it becomes to fill the remaining portion of the mold and the greater the tendency for metal shrinkage defects to occur in this portion of the casting. Moreover, since the casting yield of a mold is defined by the casting weight divided by the total mold pour weight, it is apparent that if the pouring basin can be eliminated altogether, the casting yield can be significantly increased.
Use of the above-mentioned pressure pouring vessel transfers molten metal from a vessel into a mold. However, this apparatus and method has several disadvantages associated with its use. These disadvantages include unwanted oxidation of the metal, the stopping of pouring operations to manually clean clogged nozzles, difficult flow rate control, reduced flow rate, increased metal shrinking defects and reduced casting yield.
What is needed then is a contact pouring vessel and method for pouring molten metal directly into a mold without the need for a pouring basin, and without the unwanted nozzle buildup. This will, in turn, eliminate the unwanted oxidation of the metal, eliminate the need for shutting down pouring operations in order to manually clean clogged nozzles, eliminate the difficult flow rate control while at the same time increasing flow rates, reduce metal shrinkage defects and increase casting yield. It is, therefore, an object of the present invention to provide such a contact pouring vessel.